The purpose of the experiments proposed here is to develop the SCID-hu mouse as model system for testing gene therapeutics directed at blocking HIV-1 replication. Gene therapy offers considerable advantages as a paradigm for developing AIDS therapies. The plethora of possible targets and therapeutic strategies, however, points to the need for a model system in which to test potential AIDS gene therapies prior to clinical trials which are difficult, expensive and may have unforeseen adverse consequences for human subjects. The SCID-hu mouse is an attractive model system to test anti-HIV-l gene therapies since it is the best AIDS pathogenesis model system currently available. In vitro evolved Rev binding element (RBE) RNA molecules with higher than wild type affinity - called RBE aptamers - will be used as a prototype AIDS gene therapeutic agent. These molecules, which have been provided by Dr. Andrew Ellington of Indiana University, should have anti-HIV-1 activity since they are higher affinity versions of RBE decoys which have been shown by others to inhibit HIV-1 replication in tissue culture. We will use several forms of the RBE aptamers, alone, or in the context of the entire Rev response element (RRE) expressed from various RNA polymerase II or RNA polymerase III promoters in retroviral vectors. These vectors will be used to transform cell lines and normal T-cells in vitro as well as purified human CD34+ hemopoietic progenitor cells. RBE aptamer transformed tissue culture cells will be challenged with non syncytium-inducing (NSI) and syncytium- inducing (SI) HIV-1 molecular clones and patient isolates as a preliminary test of RBE aptamer activity. RBE aptamer transformed CD34+ hemopoietic progenitor cells will be used to repopulate the human thymus/liver grafts of irradiated SCID-hu mice. These grafts will then be infected with NSI and SI strains of HIV-1 to determine whether the RBE aptamers can inhibit viral replication and pathogenesis. Other anti-HIV-1 gene therapeutic agents will be tested when the SCID-hu mouse assay system is optimized. The ultimate goal is to define which gene therapeutic strategies are most likely to work in patients so that only the most potent AIDS gene therapeutics need be tested in clinical trials. The use of this model system will hasten the process of finding an effective AIDS therapeutic agent or agents.